Name: ______Date: ______

Purpose: In Part A you will perform a micro-titration experiment to determine the relationship between the concentration and volume of an acid and those of a base needed to neutralize it. In Part B you will use this knowledge to determine the unknown concentration of a base.

Materials: Spot Plate, 0.1M HCl, 0.1M NaOH, Phenolphthalein indicator, Unknown Concentration

NaOH, eye-droppers

Pre-Lab:

1.  Write the neutralization reaction that happens when HCl and NaOH are combined.

2.  What color is phenolphthalein in an acid? ______

What color is it in a base? ______

Part A Procedure:

1.  Obtain a spot plate and carefully place exactly 10 drops of HCl in one of the spots.

2.  Add 1 drop of phenolphthalein to the spot with the HCl.

3.  Carefully add the 0.1M NaOH to the acid, 1 drop at a time, counting each drop. Notice that the color that appears will disappear if the spot plate is gently tapped.

4.  Continue adding drops of NaOH until the phenolphthalein color does not disappear. Record the number of drops that it took in the data table below.

5.  Repeat steps 1-4 2 more times.

6.  Take the average of the number of drops that you used in each trial and record that number as the number of drops of NaOH that it took to neutralize the acid.

Part A Data Table:

Drops of NaOH
Trial 1
Trial 2
Trial 3

Average Number of Drops of NaOH Needed to Neutralize the HCl: ______

Part A Analysis:

1.  What is the relationship between the number of drops of HCl you started with and the number of drops of NaOH needed to neutralize it?

2.  The HCl that you used had a concentration of 0.1M. The NaOH you used had a concentration of 0.1M. How does the relationship between the concentrations of the acid and base relate to the volume of base needed to neutralize the acid?

  1. If you started with 20 drops of the 0.1M HCl, how many drops of the 0.1M NaOH would you need to neutralize it?
  1. What if the concentrations aren’t the same? What if the acid were twice as concentrated as the base? If you started with 10 drops of 0.2M HCl, how many drops of 0.1M NaOH would you need to neutralize it?

Part B Procedure:

1.  Obtain a spot plate and carefully place exactly 10 drops of HCl in one of the spots.

2.  Add 1 drop of phenolphthalein to the spot with the HCl.

3.  Carefully add the unknown NaOH to the acid, 1 drop at a time, counting each drop. Notice that the color that appears will disappear if the spot plate is gently tapped.

4.  Continue adding drops of NaOH until the phenolphthalein color does not disappear. Record the number of drops that it took in the data table below.

5.  Repeat steps 1-4 2 more times.

6.  Take the average of the number of drops that you used in each trial and record that number as the number of drops of NaOH that it took to neutralize the acid.

Part B Data Table:

Drops of NaOH
Trial 1
Trial 2
Trial 3

Average Number of Drops of NaOH Needed to Neutralize the HCl: ______

Part B Analysis:

1.  What is the relationship between the number of drops of HCl you started with and the number of drops of NaOH needed to neutralize it?

  1. Knowing that, how is the concentration of the unknown base related to that of the acid?
  1. The HCl was 0.1M, so what is the concentration of the unknown base? ______M

Conclusion Questions:

1.  You forget to label the concentration of a bottle of potassium hydroxide, so you decide to use titration to figure it out. You place 10 drops of 1.0M HCl in a spot plate with some phenolphthalein and find that you need to add 30 drops of the potassium hydroxide to it before a pink color stays. What is the concentration of your potassium hydroxide? Explain how you know.

2.  You drop a 2000mL bottle of 16M nitric acid (HNO3) and need to neutralize it before it is safe to clean up. You have some 16M lithium hydroxide (LiOH).

  1. Write the reaction that will occur.
  1. How many milliliters of base should you add to the acid so that the spill is completely neutral? Explain your reasoning.